Dissolution at the cathode and subsequent transport of platinum to the other cell components causes catalyst degradation in proton exchange membrane (PEM) fuel cells. Deposition of platinum in Nafion membrane was observed after potential cycling under hydrogen/air conditions. The deposited Pt formed a band in the ionomer, and a straightforward model was proposed to describe its location. The predicted position of the Pt band agreed with the experimental data. A simple scanning electron microscopy-energy dispersive spectroscopy analysis was used to estimate that similar to 13% of the platinum initially in the cathode was transported into the membrane following 3000 potential cycles. (c) 2007 The Electrochemical Society.